1. Field of the Invention
The present invention relates to an engine cooling water passage structure in which a water pump, a thermostat housing, a cooling water supply passage, a cooling water discharge passage, and a bypass passage are made into a unit.
The present invention also relates to a gas/liquid separator for an engine cooling system in which cooling water supplied from a water pump is circulated through a water jacket formed in an engine main body, and a gas/liquid separation chamber for separating air from the cooling water is disposed in a cooling water passage leading to the water jacket.
2. Description of the Related Art
Japanese Patent Publication No. 4-16610 discloses an arrangement in which cooling water that has passed through water jackets provided on a pair of banks of a V-type engine is combined in a cooling water discharge passage at one end of the V banks and then supplied to a radiator via a first radiator hose. The cooling water that has passed through the radiator is supplied to the water jackets via a second radiator hose, a thermostat housing disposed on one end of the V banks. A connecting passage is disposed between the V banks, and a water pump is disposed on the other end of the V banks. Two cooling water supply passages branch out from the water pump and before the engine is fully warmed up, the cooling water in the cooling water discharge passage is returned to the connecting passage via a bypass passage and the thermostat housing without being supplied to the radiator.
In this conventional engine cooling water passage structure, elements such as the thermostat housing, the water pump, the cooling water supply passage, the cooling water discharge passage, the connecting passage, and the bypass passage are provided independently, thereby leading to problems associated with the increase in the number of components, the number of assembling steps, the space required, and the cost.
Furthermore, in a cooling system in which air that is in the cooling water is not introduced into a radiator when an engine is stopped, the air cannot be discharged through a pressure cap provided in an upper tank of the radiator. Therefore, an expansion tank equipped with a pressure cap is provided separately. The cooling water containing air is supplied to this expansion tank via an upper part of a water jacket so that the air is discharged via the pressure cap. Such an expansion tank is known in, for example, Japanese Utility Model Registration Application Laid-open No. 5-83322.
However, the expansion tank not only requires space for accommodating an increase in the volume of the cooling water due to an increase in temperature, thereby resulting in an increase in the tank capacity, but it also requires a labyrinth structure for reliably separating the air by reducing the flow rate of the cooling water, resulting in an increase in the cost.